Auguste Charles Eugène Napoléon de Beauharnais, Duke of Leuchtenberg (9 December 1810 – 28 March 1835) was the first prince consort of Maria II of Portugal.

Despite the promise of an independent principality inserted into the final treaty, the Congress of Vienna adjourned without creating a state for Eugène, so Auguste and his siblings had no inheritance.

[citation needed] He escorted his sister Amélie to Brazil for her marriage to Emperor Pedro I and was created by his new brother-in-law, Duke of Santa Cruz on 5 November 1829.

[citation needed] Maria's childhood betrothal to Dom Miguel was broken so that a more pliant husband could be found to beget a new Portuguese dynasty, one whose loyalty might prove more trustworthy if he had no other prospects, such that he would be entirely beholden for his dynastic fortune to Portugal's constitutional regime.

[citation needed] A year later Maria II married Ferdinand of Saxe-Coburg-Gotha, a nephew of the Coburg prince who had beat out her first husband in competition for the constitutional crown of Belgium.